iPad is expected to take three months, some analysts say, to reach that milestone.

Even though it may take longer to hit the 1 million units mark, analysts point to several keys to consider in evaluating its place in Apple's royal lineup.

"We believe the device will prove more successful than skeptics currently anticipate," Bill Shope, a Credit Suisse analyst, says in a recent research report. "In contrast to the iPod and iPhone, the iPad is being launched with the tailwind of a fully developed App Store and iTunes platform. We can't overstate the importance of this distinction. This limits the period of 'evangelization' for the iPad, and it provides users with instant content and functionality. The ecosystem is already in place."
Gross Profit Margins of Nearly 47%?

During the first three months after the iPad is in stores, Shope expects it to post gross profit margins of nearly 47% in the quarter that ends in June and also reach 1.08 million units sold.

For the current calendar year, he anticipates the iPad will sell 4.81 million units, whereas the iPhone is expected to sell nearly 40.7 million units and the iPod 54.1 million. In the following year, he sees the iPad nearly doubling to 8.7 million units, while the iPhone reaches nearly 52.4 million units and closes in on the iPod, which is expected to sell 54.6 million units.

While a number of analysts point to high expectations that the iPad will develop a strong new revenue stream for Apple, Trip Chowdhry, an analyst with Global Equities Research, points to an even larger role iPad will take in Apple's future growth.
"Serious Challenges" to the iPhone

"You can't look at the iPad in isolation," he says. "Apple faces serious challenges with its iPhone. If the iPad had not launched, Apple's business would be a total disaster because the iPhone is getting hurt from Google's (GOOG) Android phone. The iPad helps to balance things out."

He notes that Apple's iPhone business has historically grown 80% to 100% annually, but he expects that rate to shrink to 25% to 30% because of Android's rising popularity.

Add to that a mature iPod market that's no longer contributing gangbuster revenue and profit growth, and the significance of Apple's iPad increases demonstratively, Chowdhry says.
iPad May Dethrone the iPhone

Shope agrees. "We still don't view iPods as a critical source of revenue or profit growth for Apple in the coming years, but for now, the segment is performing much better than we previously anticipated," Shope says in his report, noting that the App Store is helping to drive "new life" into the iPod business, particularly the iPod Touch.

In sizing up the rank of Apple's three mobile "i" products, Chowdhry calls the iPod as the initial prince, which was then dethroned by the iPhone, which in turn will ultimately be replaced by the iPad.

"It's foolish to think that the life cycle of success will match the level previously enjoyed by the previous product," Chowdhry says. "The iPod enjoyed six years of unrestricted success. The iPhone three years. Today, competition is faster and smarter. Google is also working on a tablet, so the iPad may have only one year of unrestricted success."